A conventional monitor PD 102 has a coaxial structure with a fiber, and, as shown in FIG. 6, an optical signal is tapped to an optical fiber 103 of an optical module 101 to connect the monitor PD 102 by fusion bonding and, thus, to monitor an output of the optical signal (for example, see Patent Literature 1).
FIG. 7 shows a conventional example in which the monitor PD 102 is integrated in the optical module 101 (for example, see Patent Literature 2). In the prior art, the monitor PD 102 is in a form in which a PD bare chip is mounted on a carrier such as ceramic.